The bible is clear that Adam, the first man, lived only 6000 years ago. God created Adam directly from the earth on the sixth day of Creation Week. There was no evolution involved. So according to the Bible, the earth must be 6000 years old.
Christians believe the bible is the word of God. Is God a liar? Because that's not true.
Update: When Moses, under the inspiration of God, compiled the account of creation in Genesis 1, he used the Hebrew word yôm for ‘day’. He combined yôm with numbers (‘first day’, ‘second day’, ‘third day’, etc.) and with the words ‘evening and morning’, and the first time he employed it he carefully defined the meaning of yôm (used in this way) as being one night/day cycle (Genesis 1:5). Thereafter, throughout the Bible, yôm used in this way always refers to a notmal 24 hour day.
Update 2: The people who think the earth actually could be 6000 years old are idiots. The people saying my information is wrong are wrong. The bible CLEARLY STATES ADAM LIVED 6000 YEARS AGO. That's a fact.